1. Field of the Invention
The present invention relates to a magnetoresistive element, a magnetic head and a magnetic recording/reproducing apparatus, more particularly, a magnetoresistive element constructed such that a sense current is made to flow in a direction perpendicular to a plane of the magnetoresistive film as well as to a magnetic head and a magnetic recording/reproducing apparatus using the particular magnetoresistive element.
2. Description of the Related Art
In recent years, recording density is rapidly increased in a magnetic recording/reproducing apparatus such as an HDD (Hard Disk Drive). Accordingly, a magnetic head is also required to be adapted for the high recording density.
With increase in the recording density, the size of a recording bit recorded in a recording medium is diminished, and a signal magnetic field is lowered. In a conventional ring core type inductive magnetic head, the signal magnetic field generated from the recording medium is detected via the ring core by the electromagnetic induction effect. Since the signal magnetic field is detected indirectly via the ring core, it is difficult to ensure sufficient detection sensitivity.
On the other hand, a magnetoresistive head is proposed in recent years, in which the medium signal magnetic field is detected directly by utilizing magnetoresistance. The magnetoresistive head is advantageous in that the medium signal magnetic field can be detected directly by a field-sensing portion formed in the vicinity of the medium surface, which makes it possible to achieve high sensitivity.
The magnetic head used mainly nowadays includes a spin-valve type magnetoresistive element that generates giant magnetoresistance. The spin-valve type magnetoresistive film has a stacked structure of a magnetization pinned layer (pinned layer), an intermediate layer (spacer layer) and a magnetization free layer (free layer), and exhibits giant magnetoresistance that is at least two times as much as that produced by the conventional magnetoresistive film.
A so-called CIP (Current-In-Plane) structure for a magnetoresistive film is known, in which a sense current is made to flow in an in-plane direction of the magnetoresistive film using a pair of electrodes. In the magnetic head using the particular magnetoresistive film described above, a shield type construction is employed, in which a spin-valve type magnetoresistive film is sandwiched between a pair of magnetic shields each formed of a ferromagnetic material with insulator layers interposed between them.
On the other hand, a so-called CPP (Current-Perpendicular-to-Plane) type magnetic head is proposed in recent years, in which a sense current is made to flow using a pair of electrodes in a direction perpendicular to a plane of the spin-valve film. In general, the CPP type magnetic head permits improved magnetoresistance (MR) ratio, compared with the CIP type magnetic head and, thus, a higher head output can be expected for the CPP type magnetic head. In addition, the insulating layers between the MR film and the shields can be omitted in the CCP type magnetic head so as to make it possible to decrease a distance between the shields, i.e., a magnetic gap.
Now, in a longitudinal magnetic recording system, recording density is approaching its limit because of thermal fluctuation. Such being the situation, a perpendicular magnetic recording system that is tolerant of thermal fluctuation is expected to be a promising system. Thus, systems of various combinations of perpendicular recording media and shield type magnetic heads are proposed.
For example, U.S. Pat. No. 5,206,590 discloses a system in which a shield type magnetic head is applied to a perpendicular recording medium. The magnetic head disclosed in this patent is a so-called “shield type single spin-valve magnetic head” in which a single magnetoresistive film is arranged between a pair of magnetic shields. The magnetoresistive film has a stacked structure of an antiferromagnetic layer, a magnetization pinned layer (pinned layer), a nonmagnetic intermediate layer (spacer layer), and a magnetization free layer (free layer).
When magnetization of a perpendicular recording medium is detected by using the shield type single spin-valve magnetic head referred to above, a resultant output waveform is monotonously changed with respect to signal magnetization from recording bits on the recording medium, as shown in FIG. 16. Therefore, in order to obtain an output waveform as in the ordinary longitudinal magnetic recording system in which a peak appears in accordance with passage of the magnetic head over a magnetization transition, it is necessary to add a differential circuit to a readout signal processing circuit. However, the differential circuit gives rise to a problem of increased noise. In addition, the shape of the peak after the differential treatment tends to be shifted so as to give rise to a problem of increased signal error rate and another problem of a deteriorated signal-to-noise ratio. Also, as is known to the art, in order to allow the MR head of the particular shield type to be adapted to improved recording density, it is important to diminish the gap between the paired magnetic shields. In the case of the magnetic head, however, magnetoresistive film includes a thick antiferromagnetic layer so as to make it difficult to diminish the gap between the paired magnetic shields.
Likewise, a shield type dual spin-valve magnetic head in which two magnetoresistive films are formed between a pair of magnetic shields (disclosed in, for example, U.S. Pat. No. 5,705,222) has the same problems pointed out above.